An audio interface (such as a headphone jack) of an existing audio signal sending apparatus (such as a mobile communication terminal) and an audio interface of an audio signal receiving apparatus (such as an electronic signature token, an audio signal adapter device, and other audio signal receiving apparatuses which receive and process audio signals via their audio output pins) generally use a four-section interface, in which a third pin and a fourth pin are audio output pins, i.e., a left-channel pin and a right-channel pin respectively. However, a first pin and a second pin of different types of audio interfaces play different roles, that is, there are two types of audio interfaces: the first pin is a MIC pin (a microphone pin) and the second pin is a GND pin (a ground pin); the first pin is a GND pin and the second pin is a MIC pin.
As different types of audio interfaces exist, when the ground pin of the audio interface of the audio signal sending apparatus is not connected with the ground pin of the audio interface of the audio signal receiving apparatus, the audio signal sending apparatus cannot communicate with the audio signal receiving apparatus normally.
Therefore, whether for designing the audio signal receiving apparatus which can be adaptively matched with different audio interfaces of the audio signal sending apparatus or prompting a user whether the audio interface is matched by using a voice or text prompt function of the audio signal receiving apparatus, the type of the audio interface should be firstly identified in the audio signal receiving apparatus, such that the type of the audio interface of the audio signal sending apparatus connected with the audio signal receiving apparatus can be identified.
Thus, a device which can automatically identify the type of the audio interface is needed.